1974–75 Shatt al-Arab conflict

Iran had repudiated the demarcation line established in the Persian Gulf in the Anglo-Ottoman Convention of 1913, arguing that the Iran–Iraq border in the Shatt al-Arab should be demarcated according to the thalweg principle. The Kingdom of Iraq, encouraged by Britain, took Iran to the League of Nations in 1934, but the dispute was not resolved. In 1937, Iran and Iraq signed their first official boundary treaty. The treaty established the waterway border on the eastern bank of the river except for a four-mile anchorage zone near Abadan, which was allotted to Iran and where the border ran along the thalweg. In 1958, the Royal monarchy of Iraq was overthrown by a coup d'etat led by Iraqi leftists and nationalists coup d'état. 10 years later, in 1968, Arab Socialist Ba'ath Party took power after leading the coup d'état, which established the re-establihing the Ba'ath regime in Iraq. Shortly afterwards, Iran sent a delegation of diplomats to Iraq in 1969, and when the Iraqi government refused to proceed with negotiations over a new treaty, Iran withdrew the treaty of 1937. The Iranian abrogation of the 1937 treaty marked the beginning of a period of acute Iraqi-Iranian tension that was to last until the Algiers Accords of 1975.[5]

From March 1974 to March 1975, Iran and Iraq fought border skirmishes over Iran's support of Iraqi Kurds, who were engaged in an insurgency against the Arab Iraqi state for secession and the establishment of a Kurdish state.[6][7] In 1975, the Iraqis launched a major military offensive into Iran, spearheaded with tank columns. This incursion was defeated by the Iranians.[8] Several other attacks took place; however, Iran had the world's fifth most powerful military at the time and easily defeated the Iraqis with its air power, while continuing to frustrate the Iraqis at home with its arming of Kurdish separatists, with the help of its then close allies, the United States and Israel. Some 1,000 people died on the course of the 1974–75 clashes in the Shatt al-Arab region and Iraq was unable to make any progress against Iran.[9]

Consequently, Iraq decided against continuing the conflict, choosing instead to make concessions to Tehran to end the Kurdish rebellion.[6][7] In the 1975 Algiers Agreement, Iraq made territorial concessions—including the Shatt al-Arab waterway—in exchange for normalized relations.[6] In return for Iraq recognizing that the frontier on the waterway ran along the entire thalweg as per Iran's argument, the latter ended its support for Iraqi Kurdish guerrillas.[6][10]

From left to right: Mohammad Reza Pahlavi, Houari Boumédiène and Saddam Hussein in Algiers, 1975

In March 1975, Iraq signed the Algiers Accords in which it recognized a series of straight lines closely approximating the thalweg (the deepest channel) of the Shatt al-Arab waterway as the official border, in exchange for which Iran ended its support for Iraqi Kurdish separatists.[11]

Five years later, on 17 September 1980, Iraq suddenly abrogated the Algiers Agreement following the 1979 Iranian Revolution, which overthrew the Shah and established an Islamic theocracy. Iraqi President Saddam Hussein claimed that the newly-established Islamic Republic of Iran had refused to abide by the stipulations of the Algiers Accords and, therefore, Iraq considered them null and void. Tensions began to run high between the two states as Iraq's ruling Ba'ath party feared that Ayatollah Ruhollah Khomeini was attempting to export the Iranian Revolution to Iraq by inciting its Shia-majority population into revolting against the Secular- government. Five days later, the Iraqi military launched a major offensive and invaded Iran, sparking the Iran–Iraq War.[12]

• Arab–Iranian conflict
  • Iran–Saudi Arabia proxy conflict